The present invention relates to a polarizing element and an optical element that can prevent reduced contrast due to unnecessary reflected light and are suitable for forming a semitransparent liquid crystal display etc., and a semitransparent liquid crystal display using these elements.
Conventionally, when a reflective or semitransparent liquid crystal display is formed using a reflective polarizing plate that separates an incident natural light into a reflected light and a transmitted light each comprising a polarized light, a light transmitted through the reflective polarizing plate is reflected by the face of a lower layer, etc. and becomes unnecessary returned light. This decreases the level of a black display, resulting in reduced contrast. To prevent this, it has been known to provide a light-absorbing layer on the lower side of the reflective polarizing plate.
In a semitransparent liquid crystal display, however, the light-absorbing layer needs to have a light transmission property so that the visibility in a transmissive display mode through a lighting device is ensured. Thus, in the above-mentioned light-absorbing layer system, it has been difficult to prevent reduced contrast in a black display etc. in a reflective display mode.
It one aspect, the present invention relates to a polarizing element and an optical element that can form a semitransparent or other type of liquid crystal display which is excellent in contrast in a reflective display mode and also is excellent in luminance in a transmissive display mode utilizing a reflective polarizing plate.
In one embodiment, the present invention provides a polarizing element comprising a reflective polarizing plate and an absorptive polarizer, wherein the reflective polarizing plate separates an incident natural light into a reflected light and a transmitted light each comprising a polarized light, and the absorptive polarizer is arranged on one side of the reflective polarizing plate so as to transmit a polarized light comprising the transmitted light.
In one embodiment, in the polarizing element of the present invention, first, it is preferable that the reflective polarizing plate comprises a linearly polarized light separation plate, and the absorptive polarizer comprises an absorptive polarizing plate arranged so that its transmission axis with respect to the transmitted light comprising a linearly polarized light is in parallel with the polarizing direction of the linearly polarized light. In this case, it is preferable that the linearly polarized light separation plate comprises a dielectric multilayer film or a laminate of multiple thin films different in refractive index anisotropy. Furthermore, it is preferable that the linearly polarized light separation plate and the absorptive polarizing plate are fixed with each other through an acrylic adhesive layer.
In one embodiment, in the polarizing element of the present invention, second, it is preferable that the reflective polarizing plate comprises a circularly polarized light separation plate, and the absorptive polarizer comprises a circularly polarizing plate arranged so that its rotating direction with respect to the transmitted light comprising a circularly polarized light is the same as the rotating direction of the circularly polarized light. In this case, it is preferable that the circularly polarized light separation plate comprises an oriented film of a cholesteric liquid crystal polymer or a sheet in which an oriented liquid crystal layer of a cholesteric liquid crystal polymer is supported on a film substrate. Furthermore, it is preferable that the circularly polarized light separation plate and the circularly polarizing plate are fixed with each other through an acrylic adhesive layer.
In this polarizing element, it is preferable that the circularly polarizing plate comprises a quarter wavelength plate and an absorptive polarizing plate. Furthermore, it is preferable that the quarter wavelength plate comprises at least two optical retardation layers. It is also preferable that the quarter wavelength plate comprises a stretched film of a polymer.
In the polarizing element of the present invention, it is preferable that the absorptive polarizing plate comprises a polarizing film obtained by adsorbing iodine and/or dichromatic dye on a hydrophilic polymer film and stretching the hydrophilic polymer film. It is also preferable that a transparent protective layer is formed on one or both sides of the polarizing film.
Next, the present invention provides an optical element comprising the above-described polarizing element of the present invention; and (a) a quarter wavelength plate or (b) an absorptive polarizing plate and a quarter wavelength plate arranged on the side of the absorptive polarizer in the polarizing element.
That is, the optical element of the present invention comprises a polarizing element comprising a reflective polarizing plate and an absorptive polarizer, wherein the reflective polarizing plate separates an incident natural light into a reflected light and a transmitted light each comprising a polarized light, and the absorptive polarizer is arranged on one side of the reflective polarizing plate so as to transmit a polarized light comprising the transmitted light; and (a) a quarter wavelength plate or (b) an absorptive polarizing plate and a quarter wavelength plate arranged on the side of the absorptive polarizer in the polarizing element, wherein the absorptive polarizing plate has an axial relation so as to transmit a polarized light transmitted through the absorptive polarizer.
In the optical element of the present invention, it is preferable to use a polarizing element in which the reflective polarizing plate comprises a linearly polarized light separation plate, and the absorptive polarizer comprises an absorptive polarizing plate arranged so that its transmission axis with respect to the transmitted light comprising a linearly polarized light is in parallel with the polarizing direction of the linearly polarized light.
In the optical element of the present invention, it is also preferable to use a polarizing element in which the reflective polarizing plate comprises a circularly polarized light separation plate, and the absorptive polarizer comprises a circularly polarizing plate arranged so that its rotating direction with respect to the transmitted light comprising a circularly polarized light is the same as the rotating direction of the circularly polarized light. It is preferable that the circularly polarizing plate comprises a quarter wavelength plate and an absorptive polarizing plate.
In the optical element of the present invention, it is preferable that the reflective polarizing plate, the absorptive polarizer, and (a) the quarter wavelength plate or (b) the absorptive polarizing plate and the quarter wavelength plate are fixed with one another through an acrylic adhesive layer.
Furthermore, the present invention provides a semitransparent liquid crystal display comprising a liquid crystal cell and the above-described polarizing element or optical element of the present invention, the polarizing element or the optical element being arranged on at least one side of the liquid crystal cell.
According to the present invention, the function as a semitransparent reflective polarizer is accomplished utilizing the reflective polarizing plate. In a transmissive display mode, the polarization ratio through the absorptive polarizer is maintained, and a high contrast display can be achieved due to the high polarization ratio. Also, high luminance display can be achieved by the high utilization of a lighting light due to a high light transmittance. In a reflective display mode, the optical element absorbs and cuts off efficiently unnecessary reflected light (returned light), which is an external light reflected by a lighting device etc., so that reduced contrast in a black display etc. is prevented, and good display quality with high contrast is provided.